[Elecraft] K2 S meter

[G3VVT at aol.com]

Howard,
With regard to S meter readings it does appear at least with my K2  #4168 and 
a later K2 #4324 tested a few weeks back that 80, 40, 30, 20 and 17m  bands 
come out with similar sensitivity in the level required for S9 when  switched 
to the same mode and bandwidth. For 15, 12 and 10m there was a  discrepancy 
with the later serial number being slightly less sensitive. The  alignment 
appeared to be fairly well correct for both K2.
 
With the Elecraft XG1 signal generator the testing for S9 is done at  7040kHz 
with the higher level output at 50 microvolts PD (50uV PD = approx  -73dBm). 
With the AGC threshold set at 3.80V, 50uV was insufficient  to make S9 with 
both these K2. They both needed about 63uV PD to make S9  with the preamp 
switched off and were slightly more sensitive when checked  with CW at 700Hz 
bandwidth compared to SSB with the SSB filter in circuit.
 
However during testing it was found that small variations in the AGC  
threshold voltage had a substantial effect on the level required to make  S9. With 
AGC threshold at 3.80V, as noted 63uV was required for S9. Drop  this by 0.1V to 
3.70 V, only 40uV was required and again by another 0.1V to  3.60V, only 25uV 
was now needed for S9. With all of the changes in threshold  voltages the CAL 
S HI and CAL S LO needs to be reset at each step.
 
The effect noted was posted on the Elecraft Reflector though only raised  two 
replies in confirmation. Again has anybody else seen this effect of  rising S 
meter sensitivity when lowering the AGC threshold whilst testing the K2  
receiver?
 
The optimum point for the setting of the AGC threshold with my K2 #4168  came 
out at 3.70V, which meant the S meter sensitivity came out at 40uV PD for  
S9. This can be fudged to 50uV for S9 by adjusting CAL S HI if desired. Left  
mine as is for ease of S meter HI/LO setting as per the manual.
 
Assuming the alignment is correct on the K2 reported with low S meter  
sensitivity, it may be worth checking that AGC threshold has been set to at  least 
the 3.80V initial setting. Well worth checking the K2 Alignment  Instructions 
on Don, W3FPR's web site to ensure that you get everything  correct. 
 
Bob, G3VVT
K2 #4168